Abstract: A dynamic seal for a rotary shaft, the seal comprising a sleeve for being constrained in rotation on the shaft and an annular lip of polymer having a low coefficient of friction to come into sliding rotary contact with a stationary casing surrounding said shaft so that the dynamic seal provides sealing between said shaft and said casing. An annular encoder element of magnetizable polymer and presenting at least one polarized mark is secured to said sleeve and forms a support for said lip. The invention also provides a device including such a seal, and a method of fabricating the seal.